1. Field of Invention
The present invention relates to apparatus for preserving contents stored and/or transported therein by utilizing a cryogenic material. The apparatus is particularly useful for storing and/or shipping materials, such as, for example, biological samples, tissues and/or organs.
2. Description of Related Art
Cryogenic materials have been used for the storage and preservation of perishable products, such as, for example, biological materials. The materials are stored in double-walled vacuum-insulated cylindrical containers. However, conventional storage containers do not attain a very low rate of heat transmission; that is, heat leaks from the surface exposed to ambient atmosphere to the surface exposed to the cryogenic material.
For example, U.S. Pat. No. 4,821,914 describes a cylindrical storage container which may be used to store perishable materials, such as food or biological samples, for transfer in a module by the space shuttle to a space station. As seen in FIG. 1, the container 16 is formed in two parts 18 and 20, each part having an inner shell 22 and an outer shell 24 formed of a metallic material such as steel or aluminum. The outer shell 24 is spaced from and disposed around the inner shell 22. The inner shell 22 forms a storage section 52 for receiving therein perishable materials. The space between the shells 22, 24 is filled with a getter material 46 and a continuous wrap multi-layer insulation material 44, such as a MYLAR brand polyethylene film having thin film aluminized surfaces. After the two parts of the container 18, 20 are filled with the perishable material, they are connected together and a vacuum is drawn in the space between the shells 22, 24. For more stringent temperature restrictions, the container of FIG. 3 may comprise two units 118, 118, each unit comprising inner and outer shells 122, 124 formed of a glass fiber material. All of the glass fiber material is lined with a metallic liner formed from stainless steel foil. A phase change material 144, such as paraffin wax or lithium chloride, fills the cavity between the inner shell 122 and the metallic liner 132. The phase change material is charged or frozen by filling a refrigerant cooling coil 148, disposed throughout the phase change material, with a cold gas. Connected together, a vacuum is drawn in the space between the shells 122, 124. A getter material is incorporated in the space between the respective inner and outer shells to absorb trace gases.
U.S. Pat. No. 4,974,423 discloses a cylindrical double-walled insulated container for transporting frozen materials, such as frozen biological samples. The container includes a main body 1 having two compartments 4, 8. The first compartment 4 holds the frozen material to be transported, and the second compartment 8 receives and holds the refrigerant, for example, dry ice or liquid nitrogen. The second compartment 8 encircles the first compartment 4. The container may be equipped with a temperature sensor 11 and a timer 14 from which aspects of the thermal history of the frozen material during storage in the container can be determined.
U.S. Pat. No. 3,238,002 discloses an insulated liquid nitrogen-refrigerated container 1 for shipping biological materials. The container 1 has an outer wall 2 and an inner vessel 3 disposed so as to provide an evacuable space 4 therebetween. Within the evacuable space 4, an insulating material is disposed composed of alternating layers of a metallic radiant heat barrier substance 5 and a fibrous substance 6. Within the inner vessel 3 is a specimen holder 7 formed of an integral mass of sand-lime filler that retains absorbed liquid nitrogen to cool material stored in voids in the specimen holder. The container 1 is sealed by a heat conductive plug 9. A gasket 14 is provided between a cap 15 and the outer wall 2 to seal the inner vessel 3. The cap 15 is composed of aluminum providing protection for the sealing means and, if desired, accommodating spring lock fasteners for locking the cap 15 and, in turn, the plug 9 to the outer shell 2.
U.S. Pat. No. 3,167,933 discloses a double-walled and vacuum-insulated storage container 10 for storing material at low temperatures by refrigerating the same utilizing a cryogenic fluid. The container 10 has a substantially uniform three dimensional rectangular structure. The outer shell 12 is a composite structure comprising a core 21, preferably constructed of laminated material, such as plywood or Masonite, unlaminated material, such as maple wood, or a suitable metallic honeycomb structure, which is substantially completely covered with metallic sheeting 22, preferably constructed of stainless steel. The inner vessel 14 is formed of a relatively flexible metallic material that is reinforced by cross-bridging the inner vessel walls so as to prevent excessive differential between the inner vessel interior and the surrounding evacuable insulation space 20. The container 10 is closed by an insulated aluminum cover 62. In operation, liquid nitrogen is transferred from a storage vessel into the container storage space defined by inner vessel 14. The material to be stored is then inserted into the inner vessel and immersed into the liquid nitrogen.
The above described patents are representative of various systems available for preserving perishable items. Each of these systems offers varying degrees of cooling capacity and temperature control. However, none of the above described systems offers a portable self-contained container which provides a high cooling capacity and a very low-heat leak system such as is provided by the present invention.